Specialized cutting tools which rapidly shape a simple or complex profile into the surface of elongated wood stock have been in use for many years. For example, edge details, panels, tongues, grooves, and other complex profiles are formed in wood by rotating cutter heads or bodies having transverse knife edges which shape the surfaces of moving stock during finishing operations. The cutting knives are formed or finished with the desired cutting edge profile and mounted, usually at a number of positions, in the periphery of the rotatable cutter body. The cutter body or head is mounted on a drive shaft, and then rotated at high speed about an axis transverse to the direction of stock movement so that the stock is profiled as it moves past the work station.
Obviously, the knife, which is usually a flat sided element, must be firmly held so that the shaped cutting edge is precisely positioned despite the recurring impacts encountered during high speed operation. If this is not done, the milled stock will not be held within tolerances and knife edge will wear too rapidly or the knife must even come loose.
When the knife edge wears to a degree at which it must be replaced, replacement should be quick and precise. In addition, it is also advantageous to have some adjustment capability, so that different knife thicknesses and knife shapes, within limits, can be used with a single cutter body, within limits.
The problem having existed for many years, a number of different approaches have been adopted for positioning and locking such replaceable insert cutting tools. Shaped receiving mounts or notches have been provided at regular intervals about the periphery of the cutter body, with one flat side of a knife being seated against one side wall of the receiving notch, and forced against that side wall by one or more set screws. The set screws act directly on the knife or against a knife gib that distributes force more equally. A commonly used technique is to mount the set screws so that they lie along a chord across the cutter body periphery, and intercept the knife or the knife gib approximately perpendicularly. Another approach is to use a split base supporting a cutting bit having angled planar surfaces which fit in the base in such fashion that when a clamping bolt is tightened, the tool is pulled firmly down into position. A number of systems use wedges together with complementary receiver mounts so as to provide increasing force as threaded elements are directed radially or partially tangentially into the body.
All of these arrangements involve at least some of the following disadvantages:
A. They may require extensive and costly machining of the cutter body. PA1 B. They do not efficiently redistribute forces and may be too difficult to tighten and loosen. PA1 C. They may incorporate an excessive number of parts and require too much handling to permit easy tool replacement. PA1 D. They may require an excessive amount of precision machining. PA1 E. They also require too much time to effect tool replacement. PA1 F. They are not adequately adaptable to use with different knife shapes and thicknesses.
A unit which does not share all of these disadvantages and which has been used by Applicant in the past is one in which the retaining mount or pocket in the cutter head includes a threaded bore in its base, and has a pair of substantially parallel side walls, against one of which the knife is to be seated. A knife gib wedge acting against the knife at one side of the mount is itself acted against by a conic head on a retaining machine screw. The conic machine screw head is angled to match a diverging angle on the side of the knife gib. Thus as the retaining machine screw is driven into the threaded bore in the cutter body, increasing force is directed against the knife gib and hence the knife itself. While this functions in a satisfactory manner by comparison to other units, it requires maintenance of close tolerances on the knife gib and the conic head. Otherwise, it is difficult to establish a proper fit unless parts are selectively matched. Moreover, the reactive forces on the conic head, which presses against the knife gib, seek to tighten it against the support wall opposite to the knife. This is apt to result in galling of the surfaces, increasing the difficulty of knife removal and replacement. Also, the screw and gib have to be completely removed in order to replace a knife, since adequate clearance is not otherwise available.
It is therefore desirable to provide a single replaceable insert cutting tool combination which not only provides desirably firm seating under high force, but is amenable to ready replacement of the tool, while also permitting changes in knives and other parts of the assembly.